1. Field of the Invention
The present invention relates to a curable material. In particular, the present invention relates to a curable material that can be used in an organic electroluminescent device as a hole transporting layer material.
2. Descriptions of the Related Art
The organic electroluminescent phenomenon was firstly observed and studied in the 1960s (E. Gurnee et al., U.S. Pat. No. 3,172,862 (1965)). Kodark Company (US) invented an organic light emitting diode (OLED) in the 1980s and used the vapor deposition method to prepare a double layer structure of organic films (C. W. Tang, U.S. Pat. No. 4,356,429 (1987), and C. W. Tang et al., Appl. Phys. Lett. 51, 12:913 (1987)). Since then, studies of organic light emitting diode (OLED) have become popular and progressed quickly and the organic light emitting diode is applied in the technology of panel display.
Organic light emitting diodes, comprising such as polymer light emitting diode (PLED) has been wildly used in information, communication and consumer electronic products due to advantages, such as low power consumption, long service life of elements, fast reaction response, and gradually replaces the incandescent lamp and becomes a better choice for the light source of the new century.
The organic electroluminescent device 1, for example, shown in FIG. 1 comprises a substrate 11, an anode 13, a hole transporting layer (HTL) 15, an emitting layer 17, an electron transporting layer (ETL) 18 and a cathode 19. When a forward bias is applied to the organic electroluminescent device 1, the electrons and holes are injected to the device from the cathode 19 and the anode 13 respectively and is driven by external voltage energy. The electrons and holes migrate in the layer structure due to the potential difference caused by the external electrical field and recombine in the emitting layer 17 to form excitons. Then, the energy is released and the ground state is attained so that the luminescent material of the emitting layer 17 can generate a light emitting effect.
The hole transporting layer of the organic light emitting diode is responsible for transporting the holes to the emitting layer and at the same time, blocks the electrons (from the cathode) that are migrating to the anode. The hole transporting layer has advantages of reducing the driving voltage and increasing the luminous efficiency. Commonly used hole transporting layer materials have some obvious disadvantages, such as poor hole transporting ability for most of the blue or green luminescent materials due to mismatched energy levels; i.e., the difference in energy level between the hole transporting layer material and emitting material is too great. In addition, exciton quenching easily occurs at the interface between the luminescent material and hole transporting layer material, thus, reducing the luminous efficiency of the organic light emitting diode. In addition, in the process for fabricating an organic light emitting diode, particularly a polymer light emitting diode, the emitting layer is usually prepared by a spin coating method, and thus, it is necessary to use organic solvents. The structure of the underlying hole transporting layer can be easily damaged (for example, generating an uneven surface, increasing roughness or producing pores) while spin coating the emitting layer because the hole transporting layer material has insufficient organic solvent resistance. This would impede the combination between electrons and holes, then, further affecting the luminous efficiency of the organic light emitting diodes.
Based on the above, the present invention provides a curable material. When the curable material is used as a hole transporting layer material, it does not have the disadvantage of known hole transporting layer materials, and further improves the luminous efficiency of the organic electroluminescent device.